I Won a Big Prize!: The story follows four childhood friends who grew up in an orphanage: Akira, Jun, Tsukasa and Yuuto. They work hard to make ends meet, but every end of the year, they buy lottery tickets together. That year, one of the 10 lottery tickets they bought randomly won first prize! However, the winning ticket suddenly disappears, and the four friends become suspicious of each other and start looking for the culprit among themselves…